Science: Technoquest

Thursday 5 August 1999 23:02 BST

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Q Why is a scientist called a scientist?

The word comes from the Latin scire, which means "to know". A scientist is thus one who knows or learns. Before the word was first used, a couple of hundred years ago, scientists used to be called natural philosophers. "Philosophy" comes from the Greek words for "lover of true knowledge".

Q How many species of shark are there?

There are approximately 350 different species.

Q Why is it that dogs see only in black and white?

In fact, they don't; they have colour vision, but it is similar to that of red/ green colour-blind people. In human beings, the retina at the back of the eye has three types of "cone" (colour-sensing cells) - blue, green and yellow (often known as "red"). Dogs have only the blue and yellow ones, which means in practice that they are unable to detect the difference between red and green, although they can distinguish between yellow and blue. It is thought that only animals such as birds and primates, which need colour vision in order to distinguish between ripe and unripe fruit, need colour vision.

However, dogs are highly sensitive to changes in movement because their eyes have a greater than usual number of "rods" - important for black- and-white vision - which contributes to their hunting ability.

Q Why do you get dizzy when standing on top of a tall building?

For the same reason that you can easily walk along the edge of a pavement, but not along the edge of a chasm. Your eye is not used to seeing objects at a great distance where the floor should be. The perspectives that the brain expects are not there, and it causes the body to over-correct for the apparent discrepancy. The resulting confusion in brain signals, and general anxiety caused by being in a potentially dangerous situation, cause dizziness.

Q How does the cut-off switch in a kettle work?

The switch is made of a strip of three pieces of metal sandwiched together, each of which expands at a different rate when heated. Steam from the kettle goes into the switch chamber at the back of the kettle and heats up the metal sandwich. The metals' varying expansion rate makes the strip buckle, pulling out of the circuit a metal bar attached to the switch. This breaks the power supply to the kettle element, and the kettle switches off.

Q How many people have walked on the Moon?

Between 1969 and 1972, a total of 12 American astronauts walked on the Moon, before the Apollo programme was cancelled prematurely by the US space agency Nasa. The 12 travelled in six separate Apollo missions and collectively spent approximately 80 hours outside the lunar lander, during which time they collected rock samples, took photographs and set up experiments.

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